1. Field of the Invention
This invention relates to improving the tensile characteristics of heat aged articles molded from melt-fabricable perfluoropolymers.
2. Description of Related Art
Melt-fabricable perfluoropolymers are well known to have high melting temperatures. Tetrafluoroethylene copolymers with hexafluoropropylene, commonly referred to as FEP, have melting temperatures in the range of 250-255° C. and tetrafluoroethylene copolymers with perfluoro(alkyl vinyl ether), commonly referred to as PFA, have higher melting temperatures, e.g. at least about 270° C. and typically 300-305° C. These higher melting temperatures enable such perfluoropolymers to be used in high temperature applications. Unfortunately, in continuous service some degradation of the polymer occurs, which requires that the continuous service temperature be considerably below the melting temperature of the polymer. For example, the upper service temperature for PFA melting at about 300° C. is 260° C. The service temperature of the perfluoropolymer is typically determined by aging the perfluoropolymer in the form of a melt-fabricated article at temperature conditions simulating actual service such as 200° C., followed by room temperature testing of tensile properties. The deterioration of the tensile properties provides a measure of the ability of the article to survive continuous high temperature use similar to the aging temperature or less.
The need exists for melt-fabricable perfluoropolymer that exhibits improved heat aged, i.e. which exhibits lesser deterioration in tensile properties after heat aged.